A typical inductive thin film magnetic head comprises a first magnetic pole layer and a second magnetic pole layer with an electrical coil between the two pole layers. The two pole layers contact each other at one end at a back closure to form a continuous magnetic path, with a narrow transducing gap at the other end. The portions of the first and second poles separated by the transducing gap are designated respectively as the first and second pole tips. In order to write data with narrow track widths and high linear recording densities, it is necessary to provide a magnetic head with narrow pole tips. However, there are technical problems associated with fabricating a magnetic head with narrow pole tips. A key problem confronted during manufacture is the alignment of the two pole tips. Various methods have been suggested to solve this problem.
The magnetic head described above is called an inductive head. The inductive head can be combined with a data reading transducer to form a merged head.
FIG. 1 shows a prior art approach in which a magnetic head 2 is fabricated with a first pole tip 4 wider in lateral dimension than a second pole tip 6. The wider first pole tip 4 tolerates a certain degree of misalignment during the deposition of the second pole tip 6. In the magnetic head 2, the width TW of the second pole tip 6 is intended to define the track width of the magnetic head 2. However, the problem with this approach is that due to the larger width of the first pole tip 4, magnetic flux fringing beyond the width of the second pole tip 6 is unavoidable. The fringing flux, such as flux lines F emanating from the second pole 6 to the first pole 4 as shown in FIG. 1A, would result in registering a data track 8 with a width W having ambiguous track boundaries, which seriously limit the track-to-track separations on the recording medium 10.
Modern day storage products are now built with ever decreasing physical sizes and increasing storage capacities. Magnetic heads are fabricated on microscopically confined areas. To increase the sensitivity of the magnetic head, the number of coil windings can be increased. However, any increase in coil windings is restricted by the confined areas. Furthermore, the higher the number of coil windings, the higher is the resultant inductance attached to the magnetic head. A magnetic head with high inductance is sluggish in response to data writing current and incapable of operating at high frequency ranges.
Another approach to increase the writing sensitivity of the magnetic head is to increase the magnitude of the writing current. Higher writing current generates higher Joule heat which increases the burden of the magnetic heat formed in a confined space in respect to the heat dissipation. However, an overriding issue is the premature magnetic saturation encountered by the magnetic yokes in response to higher writing current.
FIG. 2 shows the hysteresis curve 12 of a magnetic material such as Permalloy (NiFe) which includes a high permeability slope of the curve 12 and low coercivity H.sub.c. Because of these characteristics, Permalloy is commonly used as the material for the magnetic yokes or tips of magnetic head. FIG. 2A is a fragmentary view of the conventional magnetic head 2 at the tip portion. When the writing current I passing through the coil 14 increases, the magnetic flux induced by the inductive coil 14 also increases. The magnetic flux which exerts coercive force on the magnetic yoke layers 16 and 18 also increases. For example, as shown in FIG. 2, when the coercivity exceeds 5 Oersteds, the magnetic yoke layers are fully saturated at 200 nanowebers and can no longer be responsive to any increase in writing current. Normally, magnetic saturation happens at the areas with the smallest physical dimensions. For instance, when magnetic saturation occurs, it first takes place at the first and second tip layers 4 and 6 and then slowly progresses to the areas with larger physical bulk, such as the yoke bodies 16 and 18. With pole tips built smaller for the purpose of writing narrow data tracks, the problem of magnetic saturation is further exacerbated.
Magnetic heads with pole tips having vertically aligned sidewalls have been proposed. U.S. Pat. No. 5,452,164, Cole et al., entitled "The Thin Film Magnetic Write Head", issued Sep. 19, 1995 discloses a magnetic head in which the vertically aligned sidewalls of the first and second pole tips are made possible by the process of ion milling through an overlying mask as a template. However, the magnetic head of Cole et at. does not address the magnetic saturation problem.
The problem of obscure data track boundaries written by a magnetic head and the problem of preventing the magnetic head from operating in premature saturation, when the head is built with a smaller physical size, need to be addressed. The problems are more intensified as storage products are now built with further reduced sizes and increased storage capacities. Data tracks written with ambiguous track boundaries seriously undermine track-to-track separations which in turn compromise the overall storage capacity of storage devices. A prematurely saturated magnetic head is incapable of operating at high frequency and is inept in performing high rate data transfer onto media with high areal densities. Accordingly, there has been a need to provide magnetic heads capable of writing data tracks with well defined track boundaries, yet made available at reasonable manufacturing costs.